Re: [PATCH v8 1/2] PM / domains: inform PM domain of a device's next wakeup

[Ulf Hansson <ulf.hansson@linaro.org>]

On Fri, 15 Jan 2021 at 17:50, Lina Iyer <ilina@codeaurora.org> wrote:
>
> Some devices may have a predictable interrupt pattern while executing
> usecases. An example would be the VSYNC interrupt associated with
> display devices. A 60 Hz display could cause a interrupt every 16 ms. If
> the device were in a PM domain, the domain would need to be powered up
> for device to resume and handle the interrupt.
>
> Entering a domain idle state saves power, only if the residency of the
> idle state is met. Without knowing the idle duration of the domain, the
> governor would just choose the deepest idle state that matches the QoS
> requirements. The domain might be powered off just as the device is
> expecting to wake up. If devices could inform PM frameworks of their
> next event, the parent PM domain's idle duration can be determined.
>
> So let's add the dev_pm_genpd_set_next_wakeup() API for the device to
> inform PM domains of the impending wakeup. This information will be the
> domain governor to determine the best idle state given the wakeup.
>
> Signed-off-by: Lina Iyer <ilina@codeaurora.org>
> Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
> ---
> Changes in v8:
>         - Update documentation. Add Reviewed-by tag.
> Changes in v7:
>         - Simplify and set next-wakeup locklessly
> Changes in v6:
>         - Update documentation
> Changes in v5:
>         - Fix commit text as pointed by Ulf
>         - Use -EOPNOTSUPP
> Changes in v4:
>         - Use PM domain data to store next_wakeup
>         - Drop runtime PM documentation
> Changes in v3:
>         - Fix unwanted change
> Changes in v2:
>         - Update documentation
>         - Remove runtime PM enabled check
>         - Update commit text
> ---
>  drivers/base/power/domain.c | 25 +++++++++++++++++++++++++
>  include/linux/pm_domain.h   |  6 ++++++
>  2 files changed, 31 insertions(+)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index 9a14eedacb92..10a960bd3204 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -423,6 +423,30 @@ int dev_pm_genpd_set_performance_state(struct device *dev, unsigned int state)
>  }
>  EXPORT_SYMBOL_GPL(dev_pm_genpd_set_performance_state);
>
> +/**
> + * dev_pm_genpd_set_next_wakeup - Notify PM framework of an impending wakeup.
> + *
> + * @dev: Device to handle
> + * @next: impending interrupt/wakeup for the device
> + *
> + *
> + * Allow devices to inform of the next wakeup. It's assumed that the users
> + * guarantee that the genpd wouldn't be detached while this routine is getting
> + * called. Additionally, it's also assumed that @dev isn't runtime suspended
> + * (RPM_SUSPENDED)."
> + * Although devices are expected to update the next_wakeup after the end of
> + * their usecase as well, it is possible the devices themselves may not know
> + * about that, so stale @next will be ignored when powering off the domain.
> + */
> +void dev_pm_genpd_set_next_wakeup(struct device *dev, ktime_t next)
> +{
> +       struct generic_pm_domain_data *gpd_data;

Looks like you have dropped one of the needed sanity checks, to make
sure the device is attached to a genpd. My apologies if I missed that
in the previous version. So you need something like this:

genpd = dev_to_genpd_safe(dev);
if (!genpd)
    return;

> +
> +       gpd_data = to_gpd_data(dev->power.subsys_data->domain_data);
> +       gpd_data->next_wakeup = next;
> +}
> +EXPORT_SYMBOL_GPL(dev_pm_genpd_set_next_wakeup);
> +
>  static int _genpd_power_on(struct generic_pm_domain *genpd, bool timed)
>  {
>         unsigned int state_idx = genpd->state_idx;
> @@ -1465,6 +1489,7 @@ static struct generic_pm_domain_data *genpd_alloc_dev_data(struct device *dev)
>         gpd_data->td.constraint_changed = true;
>         gpd_data->td.effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
>         gpd_data->nb.notifier_call = genpd_dev_pm_qos_notifier;
> +       gpd_data->next_wakeup = KTIME_MAX;
>
>         spin_lock_irq(&dev->power.lock);
>
> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> index 2ca919ae8d36..735583c0bc6d 100644
> --- a/include/linux/pm_domain.h
> +++ b/include/linux/pm_domain.h
> @@ -9,6 +9,7 @@
>  #define _LINUX_PM_DOMAIN_H
>
>  #include <linux/device.h>
> +#include <linux/ktime.h>
>  #include <linux/mutex.h>
>  #include <linux/pm.h>
>  #include <linux/err.h>
> @@ -191,6 +192,7 @@ struct generic_pm_domain_data {
>         struct notifier_block *power_nb;
>         int cpu;
>         unsigned int performance_state;
> +       ktime_t next_wakeup;
>         void *data;
>  };
>
> @@ -217,6 +219,7 @@ int pm_genpd_remove(struct generic_pm_domain *genpd);
>  int dev_pm_genpd_set_performance_state(struct device *dev, unsigned int state);
>  int dev_pm_genpd_add_notifier(struct device *dev, struct notifier_block *nb);
>  int dev_pm_genpd_remove_notifier(struct device *dev);
> +void dev_pm_genpd_set_next_wakeup(struct device *dev, ktime_t next);
>
>  extern struct dev_power_governor simple_qos_governor;
>  extern struct dev_power_governor pm_domain_always_on_gov;
> @@ -275,6 +278,9 @@ static inline int dev_pm_genpd_remove_notifier(struct device *dev)
>         return -EOPNOTSUPP;
>  }
>
> +static inline void dev_pm_genpd_set_next_wakeup(struct device *dev, ktime_t next)
> +{ }
> +
>  #define simple_qos_governor            (*(struct dev_power_governor *)(NULL))
>  #define pm_domain_always_on_gov                (*(struct dev_power_governor *)(NULL))
>  #endif
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>

Kind regards
Uffe